The purpose of this project is to define the control mechanisms of human granulopoiesis. Preliminary experiments in soft agar and long term bone marrow cultures demonstrated that glucocorticosteroids affect early progenitor cell proliferation stimulating neutrophil colony growth and inhibiting eosinophil growth. To establish the mechanism by which hydrocortisone affects proliferation, in vitro culture experiments will be performed with steroid analogues to define structure/function relationships; suspension culture studies will define the stage at which hydrocortisone affects a myeloid precursor; and to determine whether the steroids act directly on stem cell or indirectly via an effector cell, nonadherent mononuclear cells will be fractionated into T cells, B cells and null cells and treated prior to their addition to granulocyte culture. The ability to determine early differentiation steps will depend on employing antibodies to specific eosinophil proteins (e.g. lysophospholipase, eosinophil cationic protein and eosinophil peroxidase) which will distinguish committed eosinophil progenitors from neutrophil progenitors. To determine whether neutrophils and eosinophils in mixed colonies are derived from a single precursor, the glucose-6-phosphate dehydrogenase (G-6-PD) marker of mixed colonies cultured from women donors heterozygous for G-6-PD will be employed. Finally, the lymphokine specifically chemotactic for eosinophils (eosinophil stimulation promotor - ESP) will be purified to determine if this substance shares both proliferative and chemotactic activity. To study mechanisms controlling granulopoiesis is critical to understanding the elicidation of these subacute inflammatory effector cells and further offers a model of proliferation which is unique in that it examines differentiation at a relatively late stage.